The way you asked the question suggested leaving ones country not arriving in a new country
The clue: "...who migrated to a new country."
You used almost the exact same wording in your complaint about the wording.
I also think of it as a short fight, like a scuffle. Not friendly really.
A ruck's when the ball's on the ground. A maul is when it's in the hands. Both of those are passages of open play. A scrum is more 'formal', I guess. It's a way of restarting the game after a minor infringement.